The present invention relates to systems and methods for generating light, and more particularly, to systems and methods employing bi-chromatic light sources of distinct wavelength ranges for enhancing at least one visual property within at least a portion of a target area.
Outdoor lights using incandescent light bulbs have commonly been used to illuminate streets, parking lots, sidewalks, parks, and other public areas. Over the years, conventional street lights have been modified to provide functions other than illumination. For example, U.S. Pat. No. 6,624,845 to Loyd et al. discloses an apparatus mounted within a street lamp to provide surveillance using a directional antenna. However, the majority of street lights and parking lot lights still use incandescent light bulbs which result in unwanted glare, light trespass, energy waste, and sky glow. An estimated thirty percent of light generated outdoors by the aforementioned outdoor lights goes into space, flooding the skies and creating electric haze that reduces stargazing.
Many types of light sources can typically work efficiently in a narrow range of operating conditions which are governed by the physical and chemical properties of the materials used in the light source. There are only a few types of known artificial light sources such as low pressure sodium (LPS) lamps, for example, which are both highly efficient and can generate large amounts of light. While most of these types of light sources only provide quasi monochromatic light they offer utility for a number of outdoor illumination applications. Monochromatic light from LPS lamps, for example, while not enabling color rendering, can provide high visual contrast under sufficiently high illumination levels. Unfortunately, such monochromatic light is visually unappealing, with people often preferring white light generated by broadband spectral sources. Broadband spectral illumination, however, can cause undesired light pollution and environmental concerns within regions that are proximate as well as remote from the artificial night lighting.
Outdoor light fixtures incorporating light sources including incandescent, fluorescent, high-intensity discharge (HID), or LPS lamps are usually equipped with optical systems comprising reflectors, refractors, and opaque shields that redirect light or suppress unwanted light propagation. Optical systems can enable a light fixture to effectively illuminate target surfaces while reducing undesired illumination of other areas. Many highly efficient light sources such as LPS and HID lamps, however, are bulkily shaped and require large optical systems.
In addition, light pollution can be a significant concern for astronomers and conservationists. The American Astronomical Society has noted that light pollution, and in particular urban sky glow caused by directly emitted and reflected light from roadway, residential and security lighting, for example, severely impacts the ability for terrestrial astronomy.
Walker's Law is an empirical equation based on sky glow measurements which were obtained from observations of a number of Californian cities. From Walker's Law, light pollution from a city is assumed to be related linearly to the population and the inverse 2.5 power of the distance. For example, Tucson (Ariz.) has a population of 500,000 people and is located approximately 60 km from Kitt Peak National Observatory. Tucson would therefore contribute approximately 18 percent to the total sky glow at this observatory.
It has been shown that light pollution can, moreover, have detrimental environmental effects on plants and animal species, for example nocturnal mammals, migratory birds and sea turtles. For example, roadway and security lighting along the coastline of Florida has been shown to result in sometimes catastrophic reductions in the breeding success of several species of sea turtles. For example, bright lights can inhibit adult female turtles from coming ashore to lay their eggs and also lure newly hatched turtles inland rather than to the open sea.
The American Astronomical Society and the International Astronomical Union recommend several solutions for alleviating light pollution. The recommendations include controlling the emitted light via light fixture design and placement, taking advantage of timers and occupancy sensors, using ultraviolet and infrared filters to remove non-visible radiation, and using monochromatic light sources such as low-pressure sodium lamps for roadway, parking lot, and security lighting.
LPS lighting is particularly useful near astronomical observatories because the emitted light is essentially monochromatic with an emission peak at 589 nm. Narrow band rejection filters can then be used to block this region of the spectrum while allowing astronomical observations at other wavelengths. Unfortunately, LPS lamps have a number of disadvantages when used in outdoor lights. First, the LPS lamps and their light fixture housings are typically large. For example, the LuxMaster™ luminaire product series from American Electric Lighting measures from 0.75 m to 1.35 m in length for 55 W to 180 W lamps. The large anisotropic dimensions of LPS lamps can make the required light fixture optical system bulky and the device may be cost-ineffective. Furthermore, LPS lamps have poor color rendering indices (CRI) and are inferior in this regard to light sources such as high-pressure sodium (HPS) and metal halide lamps, for example. Moreover, the unnatural illumination effects resulting from LPS lamps make LPS-based roadway lighting an often undesired solution. Consequently, LPS lamps are often limited to security and parking lot lighting for industrial sites. However, light sources with better color rendering are favored whenever color discrimination is more important than energy efficiency such as for certain safety or monitoring applications, for example.
As energy costs rise and the cost of producing LEDs fall, LED lighting systems have become an ever-increasing viable alternative to the more conventional systems, such as those employing incandescent, fluorescent, and/or metal-halide bulbs. One long-felt drawback of LEDs as a practical lighting means had been the difficulty of obtaining white light from an LED. Two mechanisms have been supplied to cope with this difficulty. First, multiple monochromatic LEDs were used in combinations (such as red, green, and blue) to generate light having an overall white appearance. More recently, a single LED (typically blue) has been coated with a phosphor that emits light when activated, or “fired” by the underlying LED (also known as phosphor-conversion (PC) LEDs). This innovation has been relatively successful in achieving white light with characteristics similar to more conventional lighting, and has widely replaced the use of monochromatic LED combinations in LED lighting applications. Monochromatic LED color combinations are more commonly used in video, display or signaling applications (light to look at), as opposed to being used to illuminate an area (light to see by). As even a relatively dim light can be seen, the luminous intensity generated by LEDs in video or display applications is not a major concern.
More recently, LEDs have started to be used in high-power devices, and are no longer limited to smaller uses such as in indicator lamps. Further, LEDs are generally more energy efficient than the lighting devices traditionally used in the general illumination market. As a result, LEDs are considered an attractive alternative to traditional general lighting devices, and are encroaching on a variety of applications in the general illumination market. Light emitted from multiple LEDs having varying chromaticity can be mixed to generate white light. Despite relatively narrow emission spectra of each LED, polychromatic color mixing devices that incorporate four or more primary sources may cover the entire visible spectrum and accurately render the colors of illuminated objects. For example, an optimized quadri-chromatic red-amber-green-blue (RAGB) device has been shown to feature high values of both the general and all the special color rendering indices. Further, and notwithstanding recent advances in the field of phosphor deposition on LEDs, these devices may operate more efficiently than the phosphor-conversion white LEDs since there is no energy loss due to conversion. Additionally, these devices allow for full color control, the ability to tradeoff between qualitative characteristics (e.g. efficiency) and quantitative characteristics (e.g. color rendering, depth perception, etc.), the incorporation of internal feedback for compensation of chromaticity variations due to aging, temperature, etc., and the like, and adjustments to emitted wavelengths due to ambient light conditions, manual activation, or an automated schedule.
As a result, a need exists for an improved system and method for generating light. In particular, a need exists for a system and method that supplement primary illumination that may comprise a yellow/amber wavelength range with secondary illumination that may comprise a red wavelength range or green wavelength range. In this manner, one or more properties of the generated light may be adjusted to increase both the energy efficiency and overall lifespan of the system components while providing for an enhancement of at least one visual property during a critical period via combination of the primary and secondary illumination.
As a light source of ever increasing choice, LEDs have been packaged in numerous forms and used in lighting applications. Special control circuits have been developed to take advantage of the variability offered by the new light source and are today being offered as a solution to specific applications. In general however the design process has not zeroed in on providing the correct lighting solution. A number of LED illumination devices create “white” light by combining two or more LEDs of various wavelengths. White LEDs are also made using phosphors. The goal has not been to vary this color spectrum in real time to coordinate with the usage of the living space. The term “white” light is loosely interpreted to cover a range of illuminating light acceptable to the user for that application. HPS's yellow light has even been called white by some and the term is exclusive only of almost monochromatic sources such as LEDs and LPS lamps. The terms light spectrum, spectra, spectrum, spectral and color are used to refer to the relative spectral power distribution of the light source.
In everyday use, as dusk approaches dim twilight and nighttime darkness adversely impact our visual perception. At dusk there is poor visual contrast for driving, and our ability to accurately judge distances lessens. Also, on rainy nights, reflections from vehicles and street lights may be especially distracting. A lighting system is required that may make adjustments to the wavelengths of its emitted light in order to compensate for deficiencies in the human eye due to the specific ambient conditions. Such selection or alteration of the lighting system's emitted wavelength may provide a wide variety of other benefits in addition to improving human night vision, depth perception, and visual acuity. One such benefit may be an outdoor lighting system capable of automatically adjusting its emitted wavelengths so as not to interfere with certain light-sensitive species of animals during their respective nesting, reproduction, migration times, and the like.
A long felt need exists for a lighting system and method adapted for use in outdoor lighting situations such that the primary illumination generated by the system or method is highly energy efficient, emitted in the direction needed (reducing the amount of light lost to the sky while improving overall nighttime viewing), and augmentable with secondary illumination comprised of a distinct wavelength range, wherein such a combination of illumination sources during a critical period enhances at least one visual properties within at least a portion of the target area of the field of illumination.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.